I've kneed people into submission from the bottom like that. When the person on top goes for their own knees, they become vulnerable to reversal. Frank was cheap, but Renzo steered his head into the knees to avoid getting legally hit in the body, which is also cheap.

Frank shoved Renzo's head into the path of his knee with his forearm; you can clearly see it.

I still like watching Frank Shamrock fight, as amater fact I like Frank Shamrock. He's an excellent martial artist, and a good fighter. He may not be a nice person but is that really what you want in a fighter.